The use of bleaching agents in washing procedures and as constituents of detergent compositions is well known in the art. Thus, bleaching agents are incorporated in or sold as constituents of a major part of the commercially available detergent compositions. Important conventional bleaching agents incorporated in detergent compositions are compounds which act as precursors of hydrogen peroxide formed in the course of the washing procedure. Perborates and percarbonates are the most important examples of compounds which are employed as bleaching agents and which exert a bleaching effect in this fashion. The detailed mechanism of bleaching by means of these bleaching agents is not known at present, but it is generally assumed that the hydrogen peroxide formed during washing converts coloured substances (responsible for stains on fabric) into noncoloured materials by oxidation and that some oxidation of the coloured substances may also take place due to their direct interaction with perborate or percarbonate.
One drawback of these commonly used bleaching agents is that they are not particularly efficient at the lower temperatures at which coloured fabrics are usually washed. Their efficiency may be enhanced by the use of activators (e.g. organic acid anhydrides, esters or imides) which give rise to the formation of peracids.
Apart from being employed for bleaching stains on fabric, such conventional bleaching agents have also been suggested for preventing surplus dyes from coloured fabrics which leach from the fabrics when these are washed from being deposited on other fabrics present in the same wash (this phenomenon is commonly known as dye transfer). The problem of dye transfer, of course, is most noticeable when white or light-coloured fabrics are washed together with fabrics of a darker colour from which dye is leached during washing.
It has, however, been found that the currently employed bleaching agents, whether activated or not, are not particularly effective in inhibiting dye transfer, possibly because the rate at which they oxidize dissolved dyes is rather slow. On the other hand, peracids formed from the bleaching activators are active against dyes on fabric so as to cause discolouration of the fabric in question.
U.S. Pat. No. 4,077,768 discloses the use of iron porphin, haemin chloride or iron phthalocyanine, or derivatives thereof together with hydrogen peroxide for dye transfer inhibition. It is indicated that these compounds act as catalysts for the bleaching process whereby they provide an increase in the rate at which dissolved dyes are oxidised (or, in other words, bleached) without causing any discolouration of the dye in the fabric. However, these catalysts are destroyed by the presence of excess hydrogen peroxide which makes it necessary to control the release of hydrogen peroxide so that only the quantity of hydrogen peroxide needed to effect the inhibition of dye transfer should be present in the wash water at any time. Such controlled release of the bleaching agent may be difficult to achieve.
Peroxidase activity catalyses oxidation of a substrate (an electron or hydrogen donor such as lignin) with hydrogen peroxide.
High-molecular peroxidases (E.C. 1.11.1.7) are produced intracellularly by some microorganisms. Thus, S. Loprasert et al., Journal of General Microbiology (1988), 134, 1971-1976 describe a peroxidase-catalase from Bacillus stearothermophilus with molecular weight 175,000, and U.S. Pat. No. 4,698,306 describes a peroxidase from Coprinus with molecular weight 37,000-41,000. Also, so-called microperoxidases of mammalian origin are known; these are hemopeptides, typically with molecular weight in the range 1,500-3,000, exhibiting peroxidase activity (e.g. DE 3134526).
Use of peroxidase together with hydrogen peroxide or a hydrogen peroxide precursor has been suggested e.g. in bleaching of pulp for paper production (SE 88/0673), in treatment of waste water from pulp production (U.S. Pat. No. 4,623,465, JP-A 2-31887) and for improved bleaching in laundry detergents (WO 89/09813). Pending U.S. patent application Ser. No. 07/421,414 (filed 13 Oct. 1989) and a co-pending PCT application disclose the use for dye transfer inhibition during laundering.
It is the object of the invention to provide an improved peroxidase for these purposes. The peroxidase should be active and stable at high temperature and H.sub.2 O.sub.2 concentration, especially at alkaline conditions. It should be free of catalase as this activity breaks down hydrogen peroxide that is needed in the reaction. For better production economy, the peroxidase should be microbial and should be produced extracellularly by the microorganism in question.